Beat the butter and sugar until pale and fluffy.
Add the beaten eggs gradually while beating.
Sift together the flour, baking soda, salt, cocoa powder then fold into the butter/sugar mixture using a large metal spoon.
Fold in the chocolate chips.
Chill the mixture for 1 hour.
Preheat the oven to 160°C.
Line the baking sheets with parchment paper.
Divide the cookie mixture into equal-sized balls. Bake in the centre of the preheated oven for 15-20 minutes.
Let stand on the baking sheet for one minute then remove with a spatula to a wire rack to cool completely. Store in an airtight container.